Ultrasonic measuring device



April 20, 1965 I-I. E. DAI-ILKE ETAI. 3,178,940

ULTRASONIC MEASURING DEVICEl AGENT April 20, 1955 H. E. DAi-{LKE ETAL3,178,940

n ULTRASONIC MEASURING DEVICE Filed Jan. 8, 1958 5 Sheets-Sheet 2V WALTER WELKOW/TZ /NVE/VTORS: HUGO 5 @AHL KE BVWAZM% AGENT 5 Sheets-Sheet 3H. E. DAI-M KE ETAL ULTRASONIC MEASURING DEVICE April 2o, 1965 FiledJan.

'HUGO E. UAH/ KE www@ W MGENT April 20, 1965 H. E. DAHLKE ETAL 3,178,940

ULTRASONIC MEASURING DEVICE .WAUER WEL/@Mrz NVENTORS' Huso 5. @AHL KEAGENT April 20, 1965 H. DAHLKE ETAL ULTRASONIC MEASURING DEVICE 5`Sheets-Sheet 5 Filed Jan. 8, 1958 70 TRANSM ITTED PULSE AM PLITUDEREPETION RATE 2ms, d= +LOcm REC. TRANSDUCER 500 750 GALS, PER MIN.

n n .A .C R. CWD N ms o N n A E R P T E 2.50 560 v'r'ao GALS. PER M I N.

/NVISNTOIQSt MLTW WEL/(OW/TZ 'Hl/ Go E. @AHL KE 8V WMWGW United StatesPatent of New Jersey Filed Ian. 8, 1958, Ser. No. 707,744 10 Claims.(Cl. 7.3-194) This invention relates in general to ultrasonic measuringtechniques and apparatus, and more particularly, to owmeters formeasuring fiuid-flow in closed conduits by ultrasonic means.

Many of the older techniques and devices for measuring Huid-dow throughconduits rely on various types of mechanical and magnetic sensingsystems which include deflecting vanes or other obstructions, interposedin the channel of How. Devices of this type have the disadvantage thatthey cause a reduction in the maximum pressure of the flowing fluidthereby rendering the measurement of questionable accuracy because ofthe presence of the measuring device, and further interferring with theOperation of the system for other purposes. Moreover, another apparentdifficulty in such systems, `is the necessity for having a break ordiscontinuity in the pipe walls where the testing device is inserted.These disadvantages are overcome by the use of ultrasonic ow measuringtechniques and apparatus, wherein it is unnecessary to interpose anyparts into the channel of fiow.

However, problems also arise in ultrasonic flow measuring systems,particularly in certain types of pulse systems which utilize frequency,phase or time differences between transmitted and received pulses as theowmeasuring criteria. In many cases, these differences are, at best,small, and subject to wide variations with temperature and pressurewhich require compensation. Moreover, many types of ultrasonic ilowmeasuring equipment utilize carrier frequency oscillators, which requirecareful frequency stabilization to provide meaurernents of the requiredaccuracy. A further requirement for many applications is thatmeasurements be made in terms of mass flow rather than in terms ofvolume flow. In the ultrasonic flow-measuring devices available in theprior art, such compensations .and modifications required complex andcumbersome circuitry.

It is accordingly, the object of the present invention to providesimplifications and improvements in ultrasonic measuring techniques anddevices, thereby rendering the devices more accurate, more compact, andless costly. A more specific object is to provide am system which isreadily adopted for mass iiow measurements, and which is inherentlytemperature compensated.

These and other objects are realized, in accordance with the presentinvention, in a flow meter which relies for its operation on deflectionof a pulsed ultrasonic beam which is transmitted transversely to thedirection of fluid ow in a closed conduit. A simple pulse generator iscoupled to induce resonant shock vibrations in an electroacoustictransducer disposed on a at area on the outer-surface of a pipe sectionthrough which the fluid velocity is to be measured. A second transducerdisposed on a parallel flat area on the outer surface on the oppositeside of the pipe section receives the transmitted wave trains, which areamplified and detected. The signals are then passed through adirect-current amplifier to an indicating device. Assuming a constanttransmitted pulse, the voltage across the indicating device varies as afunction of the fluid-flow in the conduit, as a function of the positionof the receiving transducer with respect to the transmitting transducerin the direction of flow and also as a function of the sizes and shapesof the two transducers. When the transmitting and receiving transducersare at exactly opposite points on the pipe section, the output voltageis nearly constant for small variations in ow. However, it has beendiscovered, in accordance with the present invention, that if thereceiving transducer is displaced in the direction of the origin of theflow, with respect to the transmitting transducer, the direct currentoutput voltage due to the received pulses is a linear function of thefiow rate.

Moreover, it has been found that the slope of the calibration curve canbe varied by increasing the gain of the direct current amplifier in thereceiving circuit, so that, in addition to the principal transmittedpulse, the output includes a large number of reliected pulses, each ofwhich contributes significantly. The shape and slope of the calibrationcurve is subject to further variation by modification of otherparameters of the system, in a manner which will be discussed in detailhereinafter.

In accordance with a particular embodiment, the circuit of the presentinvention is so modified that the directcurrent output voltage on theindicating meter is a linear function of the mass, rather than thevolume, of uid flowing in the system. This modification of the systempermits ow measurements to be made on different fluids, withoutrecalibration of the system. Moreover, as so modified, the system isinherently temperature compensated for temperature changes in the fluid,because of the fact that the tempeature-sensitive components arecancelled out, in a manner which will be described hereinafter.

Other features of the ow measuring technique of the present inventionare that it does not involve a carrierfrequency oscillation generator,in which it is necessary to stabilize the frequency; and that, moreover,the slope and shape of the calibration curve may be modified as desiredby merely changing the gain of the direct current amplifier, theposition of the receiving transducer with respect to the transmittingtransducer, the pulse repetition rate, the shape of the receivingtransducer, or other circuit parameters.

Other objects, features and advantages of the present invention will bereadily apparent from a study of the detailed specification hereinafterwith reference to the attached drawing in which:

FIGURES 1, 2, and 3 are diagrammatic showing of the relationship betweenthe transmitting and receiving transducer positions and the form of thecalibration curve in terms of output voltage Versus iiow-rate;

FIGURE 4A is a vector plot of the sound velocity and the fluid velocity,showing the resultant velocity and the beam deection angle;

FIGURE 4B is a diagrammatic view, partly in crosssection, showing thebeam deflections in the conduit;

FIGURE 4C is a plot of signal amplitude against probe displacement,showing the peak in the amplitude at the center of the beam with nofluid flow;

FIGURE 5 is a block diagram of an illustrative circuit 1n accordancewith the present invention;

FIGURE 6A is a detailed circuit schematic of the blocking oscillatorpulse transmitter of the illustrative example under description;

FIGURE 6B shows the general form of the plate voltage in the blockingoscillator of FIGURE 6A;

FIGURE 6C shows the form of the voltage impressed across thetransmitting transducer;

FIGURE 7A is a detailed circuit schematic of the receiving andindicating circuit in the illustrative example under description,designed for volume-dow calibration;

FIGURES 7B and 7C are modifications of the circuit shown in FIGURE 7Afor mass-flow calibration;

FIGURE 8 includes several curves showing the iniiuence of thetransmitted pulseamplitude on the peak-topeak voltage of the echoes,measured on the plate of the third alternating-current ampliiier stageand the voltage on the cathode of the direct-current amplitler tube;

FIGURES 9 and 10 are curves showing the variation in output voltage withfluid low, utilizing receiving transducers of two different shapes.

The flow-measuring device of the present invention is designed tooperate in accordance with the following principle. An ultrasonictransducer positioned on the outer surface of the pipe section throughwhich the flow is to be measured is periodically shocked into resonantthickness-vibration, producing a series of ultrasonic pulses atitsrresonant frequency. If no iiuid is flowing in the pipe section, andthe beam pattern of the transmitting transducer is symmetrical about aplane perpendicular to the long axis of the pipe section, the maximumenergy portion of the pulsed beam impinges on the far side of the pipesection at a point in thesame plane. It fluid is flowing in the pipe,the transmitted pulse beam is delected downstream from this position byan angle which is a function of the velocity of the tluiddlow in thepipe section and the kind of luid, the flow `of which is being measured.

A fraction of the transmitted pulse energy travels through the pipe wallto the receiving transducer which is mounted on the outside of the pipe,opposite to the transmitting transducer, and is picked up by a receivingtransducer which is tuned to the same resonant frequency as thetransmitting transducer.

The remaining part of the transmitted pulse energy is relected from thepipe wall, and travels back and forth as a first echo, a portion againbeing reilected as a second echo, and so on, to create higher orderechoes. After each rellection, the echo amplitude decreases, the pulsetrains substantially disappearing after to 30y rellections, depending onthe absorption, refraction, etc. of the system. After the last echodisappears, another transmitter pulse is impressed on the system, andthe cycle is repeated.

Hence, the voltage on the receiving transducer consists of a continualchain of pulses, each of which is followed by a number of echoes. Thesepulses and their echoes are amplified, and rectified, resulting in anegative voltage which is impressed on the grid of a direct-currentamplifier.

The system is so calibrated, that under the condition of no-tlow,sufficient negative bias is applied to hold the direct-current amplifierat the cut-off point. With increasing tlow, the negative bias isreduced, since the number and the amplitude of echoes decreases causingcurrent to flow in the cathode resistor of the direct-current amplifier,producinga cathode voltage which is read on the direct-current read-outmeter.

It has been observed that increase or decrease in this voltage is afunction of the position of the receiving transducery relative to thetransmitting transducer in the direction of lluid flow in the pipesection.

In the system shown in FIGURE 7A, the output voltage across theindicating meter varies in terms of volume flow in the conduit; whereasin a system modilied in the manner indicated in FIGURES 7B and 7C, theVoltage across the indicating meter varies in terms of mass low.

Referring to FIGURE l of the drawings, TT represents the transmittingtransducer, and TR represents the receiving transducer.

In the case illustrated in FIGURE 1, the receiving transducer is mounteddirectly opposite the transmitting transducer, the line of normalincidence passing through the center of both transducers. When theoutput voltage of the direct-current amplifier is plotted against flow,for this configuration, it is seen that the curve remains relativelyflat for a considerable range of llow velocities.

In the case illustrated in FIGURE 2, the center of the receivingtransducer is displaced in the direction of CJD Cil

llow, a distance of, for example, about 1/2 inch for a pipe with 3 inchinside diameter with respect to the transmitting transducer. The outputvoltage, when plotted against the tlow-velocity', decreases to a minimumand then increases.

In the )case sho-wn in FIGURES, the receiving transducer is displacedupstream with respect to the transmitting transducer, a distance of, forexample, about M2 inch for a pipe with three inch inside. diameter. Inthe latter case, the output voltage varies linearlywith changes in flowvelocity. It is apparent that to enable the receiving transducer'toreceive the transmitted beam direct- .ly and a large number of echoesthereof that the receiving -transducer is spaced only slightly upstreamfrom the transmitting transducer where it is well Within the direct beamof the transmitted wave.

If the ultrasonic beam is initially directed perpendicular to the. pipeaxis, under a condition of no-flow, the maximum energy rellection pointsfrom the opposite side of the pipe may easily be determined, as afunction of the fluid velocity from the following considerations.

Let:

Vs=sound velocity in the fluid Vf=tluid velocity w=angle of dellectiondzinsidediameter of the pipel L1=distance of the first rellection pointof the beam under a condition of flow, from the rellecting point atno-flow.

Ln is the distance corresponding to the nth reflecting point; and

n is any odd integer.

From FIGURE 4A, it will 'be apparent that when tluid is ilolwingrin thepipe, an'impressed ultrasonic pulse will travel at a velocity which isthe vector resultant of Vf and Vs.

Referring to FIGURE 4B:

tan @Vlg 1) tan =L1 (2)- Vsl 3) Lgvs 4) In FIGURE 4B: the angle is theadditional amount of beam deflection after the first reflection; theangle y is the additional amount of Ibeam dellection after the secondreflection; .the angle is the additional amount of beam dellection afterthe third reflection; and the angle e is thel additional amount of beamdellection after the fourth reflection.

From FIGURE 4B; since-the angles of incidence and reflection are equalat each contact of the beam with the pipe wall and since the )beam isdisplaced 4by an additional amount after eachrellection, we get:

In similar manner, it can -be shown that each subsequently added angleis likewise equal to oc.

Referring to FIGURE 4B, it can be seen that the angle the beam makeswith the wall of the pipe on the side from which the first transmissionacross the pipe is taken is given as follows:

Angle of initial crossing is a.

Angle of second crossing is 2a.

Angle of third crossing is 3a.

Angle of nth crossing is nu.

The beam shift from the point of beam origination after each crossing isgiven as follows:

After the initial crossing, it is L1.

After the second crossing, it is 3L1i=L2i2L1.

After the third crossing, it is 6L1=L3+2L2+3L1- After the fourthcrossing, it is lLlzLr-l-ZLS-l-SLZ-{ALL After the nth crossing, it is n50M-D131 (12) Since the receiving transducer is oppositely placed on thepipe from the transmitting transducer, signals may be received only onodd numbered crossings. nals so received may be defined as echoes asfollows:

The Isecond echo is the pickup after the third crossing.

The third echo is the pickup after the fifth crossing.

The nth echo is the pickup after the (2n-1) crossing.

We define the beam shift of each echo with the letter S and thesubscript number of the echo and combining (12) and (13) we get:

The shift of the first echo=S1i=L1.

The shift of the second echo=S2=6L1- The shift of the thirdecho=S3=15L1.

The shift of the nth echo=Sn=ni(2n-1)L1.

The pulses picked up by the receiving transducer, after passing throughseveral stages of alternating current amplification, are rectified andimpressed on the grid of the direct current amplifier as a bias.Decrease in this bias, as it occurs with increasing flow permits thedirect-current amplifier to conduct, so that the voltage across itscathode resistor increases Iwith increasing iiuid-flow. Thedirect-current output characteristic has lbeen found to be a function ofthe shape, size, and position of the transducer, and also, of theadjustment of the transmitter and receiver, as well as of the relativepositions of the transmitter and receiver.

As previously pointed out, an important feature of the `system of thepresent invention is that the circuit can be modied so that the outputvoltage varies as a linear function of mass How, rather than volumeilow, thereby providing a uniform calibration for all liquids in termsof pounds per minute. This modification has the advantage that iteliminates the necessity for temperature compensation in the fluidconduit.

Such a modification is based on the following theoreticalconsiderations:

Let a equal the amplitude of a received signal.

Then, referring to FIGURE 4C, which shows diagramfmatically thevariation of signal amplitude with Abeam displacement:

The sigwhere e0 equals the output voltage on the receiving transducer ina liquid of density p and sound velocity VS.

Substituting from Equation 15:

@Darse-prani 17) From the above, it is seen that the Vs term balancesout in the second term; hence, this term is independent of soundvelocity in the fluid. Accordingly, in order to make the output voltageindependent of sound velocity, and a function of mass flow, rather thanof Volume flow, it is necessary to add to the output voltage a termwhich is equal to, but opposite in sign, to the rst term of Equation 17.Such a voltage, proportional to pVS, is derived at the input to thetransmitting transducer, since the static capacitance of the latter hasbeen balanced out to provide a resistive load. This is fed directly intothe direct current output, of the receiver adjustment being made under acondition of no fluid flow in the conduit to give a zero reading at theoutput meter. Accordingly, under a condition of fluid flow, the outputmeter reads the following voltage:

Where r3 is a constant.

STRUCTURE FGURE 5 shows, in block diagram, the circuit arrangement for apreferred embodiment of the How-meter of the present invention. Thisincludes the transmitting circuit 1, the transducers 2 and 4 mounted onpipe 3, and the receiving circuit 5.

The transmitter 1 is connected across the electrodes 2a, of 4thetransmitting transducer which are evaporated and fired on or otherwiseattached, to the opposite major surfaces of a piezoelectric transducer2. The transmiting transducer 2 and the receiving transducer 4 on theopposite side of the pipe, may comprise any of the types piezoelectriccrystalline elements well known in the art, constructed to vibrate in athickness mode, such as, for example X-cut quartz, or thin sheet bariumtitanate ceramic, processed and polarized in the manner set forth indetail in Patent 2,486,410 issued to Glenn N. Howatt dated November 1,1949. In accordance with one form the transducers are flat wafers aboutmils thick, and inch in diameter, vibrating in a resonant thickness modeof about one megacycle. These are coupled to a ilat portions 3a and 3bof a pipe section 3. In the example under description the latter isabout six inches long, and has an inner diameter of 3 inches, and outerdiameter of four inches. The coupling to ats 3a and 3b may be made bymeans of any satisfactory medium of matching acoustic impedance, such asan epoxy system in which the base resin is combined with a hardener,such as, for example, metaphenylene diamine, and inert mineral fillers.Portions 3a and 3b are machined flat and parallel to within about a mil.The Wall thickness is .206 inch, and is uniform over the extent of theportion to which the transducers are attached. This thickness is a halfwave length in the one megacycle frequency of the transducers within atolerance of about one mil. Pipe section 3 terminates in a pair offlanges designed to fasten the unit into the fluid pipe system.

Whereas in the embodiments under description, the transmittingand'receiving transducers are both round, fiat wafers, in aiternativeembodiments they may be cut in other shapes, each of which producesadifferent characteristic curve relating `output voltage to the rate ofuid flow in the conduit. A practical shape for the receiving transducershas been found to be aflat, triangular wafer, two sides of which are 3/8inch, and one side,

1/2 inch. allel to the direction of iiow in the conduit.

In the present illustration, the transducer d on the opposite side ofthe pipe is displaced about l centimeter withrespect to the transducer 3in a direction opposite to the direction of iow.

The signals receivedv by the transducer 4 are conducted.

by afcoaXial cableto the receiving circuit 5 where they are amplifiedand rectified, the rectitied output passing Ito a meter 6.

In accordance with a further feature of the invention, the .gainof thedirect-current amplifier of the receiving circuit 5 can be adjusted sothat any given flow rate, over the range, for example 100 to 1000gallons per minute, can produce any desired output voltage, made up notonly of `the primary received signal, 'but up to as many as or 20 echoesof the received signal. This provides a direct-current output whichvaries with changes in fluid-flow, in accordance with a linearcharacteristic, the slope of which may ybe modified by including a largenumber of echoes in the direct-current out-put. The circuitcontiguration willnow be described in detail.

T ransmfter circuit Considering the transmitter circuit of FIGURE 6A,the first stage is a free-running blocking oscillator. This includesapentode 7, having a control grid 8, a screen grid 10, and a suppressorgrid 9 connected toy a Cathode 11, and a plate 12. The screen 10 isenergized from the 300`vo1t positive source 2.3 through a sliderconnected across the 250,000 ohm potential divider 15, an alternatingcurrent path to ground being provided by the 0.05 micro-farad capacitor24. The plate 12 is coupled to both the control Agrid 8 and the cathode11 through the primary coil 18 of a pulse transformer 17, having aoneto-one turns ratio to a pair of secondary coils, 19 and 20. Thetransformer 17, which has a reactance within the microhenry range, ischaracterized by a very fast rise time, for example, about 0.2microsecond, and is constructed to withstand peak-to-peak voltageswithin the range 200 to 400 volts. One terminal of coil 19 is connectedin series withthe '.004 microfarad capacitor 16 to control 2.5 megohmvariable resistor 13 in series with the 0.63 f

niegohrn resistor 14.

One terminal of the coil 20 is connected directly to the cathode 11,While the other terminal thereof is connected thro-ugh the 0.01micro-farad capacitor 26 in the direction of easy flow to the positiveterminal of the rectitier 25, which may comprise any tube diode orselenium rectifier having a good front-to-back ratio and which isadapted to withstand up to about 100 Volts maximum positive or negative.The reverse terminal of rectifier 2.5 is connected to the control gridy28 of pentode 27, of the cathode-follower amplifier stage, across a100,000 ohm grid resistor,` 39.

In addition to the control grid 2S, the pentode 27 includes suppressorgrid 29 directly connected to the cathode 31, a screen grid 30, and aplate 32.' is energized through a,2,700 ohm resistor 37 and an 11,- 000ohm resistor 3S by the 300 volt positive potential This is mounted withthe 1/2 inch side parl The plate 321- llt) `:source '23; and the screengrid 30 is energized through the t10,000 ohm resistor 341, alsoconnected to the 11,000 Aohm :resistor 38, and the positive source 23.An alternating current path directly to ground from the plate 32 isprovided throughY the .05 microfarad condenser 36; and from the screen30 through the 0.05 microfarad capacitor 33. In addition, the junctionbetween the resistors 34, 37, and 38 is connected to ground through the0.03 microt'arad capacitor 35;

` The cathode 31 is connected to ground through the ohm resistance 40;cathode 31 is also connected in .the direction of easy current iiow tothe rectifier 41 .through the inductance 44 .variable over themicrohenry range. The other terminal of Vrectilier 41 is connectedthrough the one megohm resistor 42 to ground. The ,junction betweeninductance 44 and' one terminal of rectifier 411 isV connected throughthe central conductor of a coaxial cable coupling to one electrode. 2aof the transducer 2 mounted on the frate portion v3a on one side of thepipe section 3.

The pipe section, in contact with` the second electrode of thetransducer 2, is connected to the grounded outer conductor of the cable43.

The transducer 4 is displaced one centimeter upstream in the directionof flow in the pipe 3. As previously explained, the direct-currentoutput Voltage is a function of the position of the receiving transducer4 with respect to the transmitting transducer 3 in the direction offluidflow, the shape of the output voltage curve Versus fluiddow beingsubject to the relative positions of the transmitting and receivingtransducers, as indicated in FIG- URES l, 2 and 3.

Receiver Referring to FIGURE 7A the receiving circuit comprises threeradio frequency ampliiier stages, a rectifier, a direct currentamplilier, and a direct-current meter.

The electrodes 4a of the transducer 4 are connected by means of acoaxial couplingcable across the primary winding 47 of the transformer46, which is coupled to the input of the first stage of amplification.Primary winding t7 comprises l5 turns of the number 36'enamel wire, thelower terminal being grounded. The secondary coil 48 of the transformer46, which comprises 100 turns of number 36 enamel'wire, is connected inparallel with the 100 microctarad capacitor 49, to provide a tunedcircuit across the control grid 51 of the pentode 50". In addition tothe control grid 51, the pentode tube 50* comprises a suppressor grid53, directly connected tothe cathode 54, a screen grid S2, and a plate55. The plate is energized from the volt .positive potential source 59through a 4,700 ohm resistor 64 in series with a tuned circuit whichcomprises the inductance 62, variable over the range 250 to 350microhenries, parallel with the 100 micro-microfarad capacitor 61. Thescreen 52 is energized lfrom source 59 through the 22,000 ohm resistor58; and screen 52 is connected to ground through the .05

microfarad capacitor 57. The cathode 54 is connected to thelow-potential-terminal of the coil ri'through 1,000 ohm variableresistor 56, and also to the low potential terminal of the tuned circuitcomprising coil 62, and capacitor 61, through the 0.05 microfaradcondenser 63.

The plate output circuit or" the pentode 50' connects to a second stageof radio frequency amplification, which includes the pentode 66, through`a 0.01r microfarad coupling capacitor 65,'wl1ich is connected to thecontrol grid 67 across the 47,000 ohm grid-leak resistance '72 toground. The tube 66 also includes suppressor grid 69, directly connectedto the cathode 70, screen grid 68, and plate 71.

The plate 71 is energizedl from the positive potential 150 volt sourceS9, through the 47,000 ohm resistor '79 in series with a tuned circuitincluding the 100 micromicrofarad capacitor 76 and the inductor 77variable over the 250 to 350 microhenry range. The screen 63 isenergized from the same 150 volt potential source 59 through a 22,000ohm resistor 75; and is connected to ground through the .05 microfaradcapacitor 74. The cathode 70 is connected to ground through the 1,000ohm variable resistor 73.

The output circuit from plate 71 in the second stage of amplification iscoupled through the 0.01 microfarad capacitor 80 to the control grid 82of the pentode 81 in the third stage of radio frequency amplification,across the 47,000 ohm grid leak resistor S7 to ground. The pentode 81comprises, in addition the supressor grid 84 directly coupled to cathode85, the screen grid 83, and the plate 86. The latter is energized frompositive 150 volt source 59 through the 47,000 ohm resistor 95 in serieswith a tuned circuit, including the 100 mcro-microfarad capacit-or 92 inparallel with the variable inductor 93, the latter being connected toground through the .05 microfarad capacitor 94. The screen y33 isenergized by the same 150 volt source 59 through the 22,000 ohm resistor90, a connection from the screen 83 to ground being provided through the.05 microfarad capacitor 89.

The output circuit from plate 86 is connected in the direction of highresistance to rectifier 97 through the .05 microfarad coupling capacitor96, across the 470,000 ohm resistor 91.

If, as shown in FIGURE 7A, the device is to read in terms of volumefiow, velocity then the arrangement is as follows.

The output from rectifier 97 passes thru a potential divider consistingof the 1 megohrn resistor 103, which is connected in series to thecathode 100 of triode 98. A slider connects a portion of resistor 103 inseries with the ten thousand ohm resistor 102 to the control grid 99 oftube 98. The .05 microfarad capacitor 104 connects the slider to ground;and the .5 microarad capacitor 105 connects grid 99 to ground.

In addition to cathode 100 and grid 99, the triode 9S, thedirect-current amplifier stage includes the plate 101, which isenergized by the positive 150 volt source 59 through the 10,000 ohmresistor 106. The plate 101 is coupled through the .05 microfaradcapacitor 107 to ground. The cathode 100 is connected to ground throughthe 25,000 ohm Variable resistor 108, which is in parallel with the .05microfarad capacitor 110, and the one megohm potential divider 109. Aslider 113 is connected across the latter for the purpose of adjustingthe directcurrent read-out. The entire output across potential divider109 is impressed across the 100,000 ohm variable resistor 111 in serieswith a conventional direct-current meter 112, the negative terminal ofwhich is grounded. As previously stated, for the embodiment justdescribed, the direct-current meter 112 is calibrated in terms of volumeflow velocity.

If it is desired to measure mass-flow, velocity instead of Volume iiow,velocity and to have a system in which it is possible to measure theiiow-velocity of diierent types of liquids, without recalibration, thenit is necessary to modify the system of FIGURE 7A in the mannerindicated by FIGURES 7B and 7C of the drawings.

In FIGURE 7B, the variable inductor 121 has been interposed in thesection to the left of the dotted line WW and to the right of line XX,in FIGURE 7A, between the connection to receiving transducer 4 and thehigh potential terminal of the primary coil 47 of transformer 46. Thepurpose of this addition is to balance out the static capacitance ofreceiving transducer 4.

Referring to FIGURE 7 C, the input circuit to the directcurrentamplifier in the circuit of FIGURE 7A has been modified between thedotted lines YY and ZZ by adding a feed-in circuit to impress on thereceiver output circuit a component of voltage derived from thetransmitter, for the purpose of the balancing out the pVS term from thereceiver output, voltage in the manner set forth in detail hereinbeforewith reference to Equations 17 and 18.

This circuit includes a slider connected to potential divider 42, in thetransmitter circuit FIGURE 6A through the half megohm resistor 122 tothe junction between the half-megohrn Variable resistor 123, and theterminal b of single-throw switch 127. The common terminal of the latteris connected to the junction of the half-megohm fixed resistor 102, andthe one-megohrn variable resistor 103. The terminal a of switch 127opens the circuit, both from the rectifier 97 and from the feed-incircuit from the potentiometer 42 in the transmitter circuit. Theparallel connected capacitors 104 and 105 have the values .01 and .5microfarads, respectively;

The grid 99 is biased negatively through the one megohm resistor 124connected to the 110,000 ohm potential divider 126, across the 108 voltnegative terminal of potential source 125.

OPERATION In the transmitting circuit, when the energy from the positivesource 23 is applied to the plate 12 of the blocking-oscillator pentode7, the latter, at first becomes conducting, producing a positive surgeof output current. This charges up the condenser 16 in a direction todrive the control grid 8 below cut-ofi, whereupon pentode 7 ceases toconduct. The negativecharge gradually leaks off the grid 8 thru the gridresistor 13, until the grid again is raised about cut-off and the cyclerepeated.

The voltage variations with time, of plate 12, are indicated in FIGURE6B of the drawings. The negative portion of the characteristic is cutoff by the diode 25, so that only the positive pulses are impressed onthe grid 18 of the pentode 27.

The repetition-pulse rate of the blocking oscillator, which can beadjusted by means of the grid resistor 13, is about 2 milliseconds inthe present illustrative embodiment. The pulse-width, of the positivepulse which in the present embodiment is about one microsecond, is afunction of the time constant of the transformer 17, which is about 0.2microsecond.

Power-output pentode 27, which is connected as a cathode follower,functions first, to decouple the output ot the transmitting transducer 2from the blocking oscillator; and secondly to amplify and broaden thepositive output pulse which is impressed across the transducer 2.

When the positive output pulse from the blocking oscillator, isimpressed on the grid 2S, it drives the pentode 27 into conduction. Theresulting positive pulse derived from the cathode resistor 40 isimpressed across the transmitting transducer 2, thru coaxial cable 43,shocking .the transducer into resonant vibration at about 1 megacycle,so that it transmits an ultrasonic pulse about 10 microseconds longacross the stream of liquid iiowing in the pipe section 3.

The reactance of coil 44 is adjusted to tune out the blocked capacitanceof transmitting transducer 2, thereby presenting a resistive loadthereacross, which is useful in case of a mass-flow calibration, aspreviously described.

The transmitted pulse from transducer 2, together with fromtwenty-to-thirty echoes, is received by the receiving transducer 4, andimpressed through the coaxial cable on to the primary coil 47 oftheimpedance-matching tuned transformer 46, the secondary coil 48 of whichgoes to the grid of tube 50 in the first alternating-current amplifierstage.

All three alternating current amplifier stages, including tubes 50, 66and 81, include plate circuits which are tuned to the one megacycleresonant frequency of the transducers 2 and 4. The second and thirdstages, including tubes 66 and S1, can be overdriven for approximatelythe first 10 echoes of the received pulses. The gain in each of thestages is controlled by variation of the respective cathode resistors,56, 73, and 8S.

The diode 97, with its lter network including capacitors 104 and 105,and resistors 103 and 102, serves to provide a negative, direct-currentVoltage which is a arras/io l l function of the number, amplitude, andwidth of the echoes, and the repetition rate of the transmitted pulses.The function of thev filtering circuit is to eliminate transientfluctuations due to turbulence in 'the pipe. amplitude of thedirect-current output voltage is adjusted by varying the load resistancew3 to bias the grid s@ of triode 98 at cut-olf which in the presentexample may be some preselected small current such as l0 microarnperesunder a condition of no liquid iow in the conduit. With increasing flow,the number and amplitude of echoes received by. the transducer 4decreases, resulting in a decreasing negative grid-voltage. This causestriode 98 to conduct, and produces a voltage across the cathode resistorE08 which increases with increasing flow. This output' voltage isimpressed on the meter- H2, which may be calibrated in terms of volumeiiow velocity (gallons-perminute) for the circuit as shown in FGURE 7A,or in terms of mass-How velocity (6 pounds per minute) for the circuitmodiied in the manner shown in FIGURES 7B and 7C.

ln the latter case, with switch m7 open, in a position, and under acondition of no-iow in the conduit, the slider on potentiometer 126 isadjusted to bring the voltage on grid 99 to cut-off (that is, at acurrent of, for example, l() microamperes) for tube $8. Then, withswitch 127 in b position, and a condition of rio-liow in the conduit,the slider on potentiometer i2 is adjusted to bring the voltage on tube98 again to cut-oil, as above. As previously explained, this cancels outthe pVS factor from the output voltage, as indicated by Equations liland 1li, so-that under a condition of iiuid ilow, in the conduit, andwith switch 127 closed-in position b, the output meter il?. now reads interms of mass-flow velocity (pounds per minute).

The following precautions should be observed in installing theflow-meter pipe in a system in which the flow is to be'rneasured.

(l) The llowmeter pipe should preferably be installed in-a straightsection of pipe so that its distance from an elbow is at least 6 feet.Any decrease in this distance may result in inaccurate readings duc toturbulence in the pipe.

(2) The inside diameter of the ilovvmeter pipe should be aligned withthe inside diameter of the feed pipe to avoid turbulence.

(3) The iiowmeter pipe 3 should be mounted so that the center linebetween the transmitter and receiver transducers is approximatelyhorizontal to avoid gas bubbles from assembling on the inside ilats ofthe flow-meter pipe 3.

Referring to FIGURE 8 of the drawings, there are shown four curves, 21'thru 124', which respectively represent the peak-to-peak plate voltageson tube Si due to 'the lst, 2nd, 3rd, and 4th echoes of the transmittedultrasonic pulse, which vary as a function of the amplitude of thetransmitted pulse, the latter having been changed by varying voltage onthe screen of tube '7 in the blocking oscillator in the transmittingcircuit. Additional echoes, up to twenty or thirty, produce increasinglylinear characteristics on the plate of tube 81.

Curve 125 shows the direct-current output voltage taken across thecathode resistor ltlS, due to a composite including up to twenty orthirty echoes.

Curves 126 and H27' in FGURES 9 and 10 respectively show variations inoutput voltage from rectifier 97, utilizing in the former case, areceiving transducer which is a thin wafer about 10G mils thick, themajor surface of which is circular, having a diameter of 3A; inch; andin the latter case, a transducer of the same thickness which istriangular, two sides being inch, and one side 1/2 inch. In thepreferred example under discussion, the triangular transducer isvmounted so as to have the larger edge of the triangle perpendicular toand symmetrical with respect to the direction of iluid flow in theconduit.

In each of the cases illustrated in FIGURES 9 and l0,

Thev

the pulse-repetition rates were 2 milliseconds, and the transducers weredisposed with their centers displaced about 1 centimeter in thedirection of flow with respect to the transmitting transducers, whichwere circular wafers.

It is accordingly apparent that transducers of other shapes than thosespecifically shown can function successfully for the purposes of thepresent invention. For example, pear shaped transducers have also beenused with some success, for this purpose.

While specific structures have been disclosed to illustrate theprinciples of the present invention, it will be apparent to thoseskilled in the art that the scope of the present invention is not to beconstrued as limited `to any particular structure or circuitconfiguration shown herein by way of example. f

What we claim is: Y

l. A system for measuring iiuid flow in a conduit, said system includinga vibration transmitting and a vibration receiving transducer coupled tosaid conduit, said transmitting transducer being oriented to direct avibration beam substantially transversely across the conduit in theabsence-of liuid iiow, means for energizing said transmitting transducerintermittently togenerate a pulsed vibration wave beam, means coupled tosaid receiving transducer and responsive to the amplitude of thereceived wave, said receiving transducer being displaced a shortdistance from said transmitting transducer along the principal axis ofsaid conduit in the direction of the origin ofthe flow of the fluidthrough the conduit where it intercepts the vibration wave pulsationsdirected transversely of the conduit and echo pulsations thereof, theamount of vibration energy received by the receiving transducer varyingsubstantially with the change in the flow of the fluid as the vibrationwave beam isfdeiiected by the movement thereof, and a fluid iiowindicating means coupled to said receiving transducer and-responsivetothe output of said receiving transducer for indicating fluid iiow.

2. The measuring system of claim l wherein said receiving transducer ispositioned on the opposite side of said conduit from said transmittingtransducer so as to receive the vibration wave beam directly from saidtransmitting transducer before the same has been reiiected by theconduit walls.

3. The measuring system of claim l wherein said receiving transducerintercepts and is responsive .to at least one echo of each transmittedwave pulsation received after the directly received wave pulsation.

4. The measuring system of claim l wherein the spacing betweensuccessively generated wave pulsations is such that the receivingtransducer receives at least one echo pulsation reliected from theconduit Walls in addition to the first received pulsation beforereceiving the pulsation from the next transmit-ted wave.

5. A system for measuring fluid ow in a conduit comprising: vibrationtransmitting and receiving transducers coupled to said conduit, saidreceiving transducer being positioned with respect to said transmittingtransducer to provide an output which is a measure of the uid flow rate,an energizing circuit for said transmitting transducer including apulse` generating circuit for providing pulses at a r'ixed pulserepetition rate, means responsiveto the pulse output of said pulsegenerating means for intermittently energizing said transmitingtransducer at the fixed pulse repetition rate of said pulse generatingcircuit, said transmitting transducer being oriented to direct avibration wave beam substantially transversely to the principal axis ofthe conduit in the absence of iiuid flow, said receiving transducerbeing spaced from said transmitting transducer a distance measured alongthe principal axis of the conduit which is within the beam of thetransmitted wave, wherein it receives a relatively large number ofvibration wave pulsations reected from the wall of the conduit for eachvibration wave pulsation transmitted by said transmitting transducer,said received pulsations having a magnitude which varies with the rateof fluid flow, and a iluid tlow indicating means coupled to saidreceiving transducer and responsive to the output of said receivingtransducer for indicating uid ow.

6. The measuring system of claim 5 wherein the spacing betweensuccessive pulsations generated by said pulse generating means `and theresulting vibration Wave pulsations of said transmitting transducerbeing such that the receiving transducer receives at least one echopulsation reliected from the conduit Walls in addition to the lirstreceived pulsation before receiving the pulsation from the nexttransmitted Wave.

7. The measuring system of claim 5 including detecting means coupled tosaid receiving transducer and comprising rectifying and averaging meansfor producing a direct current output which is a function of the averageamplitude of the received signals.

8. A system for measuring fluid ow in a conduit, said system including avibration transmitting and a vibration receiving transducer coupled tosaid conduit, said transmitting transducer being oriented to direct avibration beam substantially transversely across the conduit in theabsence of fluid flow, means for intermittently energizing saidtransmitting transducer to generate spaced vibration wave beampulsations, flow indicating means coupled to said receiving transducerand responsive to the amplitude of the received Wave, said receivingtransducer being displaced slightly from said transmitting transduceralong the principal axis of said conduit Where the Vibration energyreceived by the receiving transducer varies substantially with thechange in the tlow of the iluid and multiple reflections of thetransmitted pulsations are intercepted thereby.

9. The measuring system of claim S wherein said receiving transducer ispositioned on the opposite side of said conduit from said transmittingtransducer so as to receive the vibration wave beam directly from saidtransmitting transducer before the same has been retlected by theconduit Walls.

l0. The measuring system of claim 8 wherein the spacing betweensuccessively generated wave pulsations is such that the amplitude of thereceived echoes of a transmitted pulsation received by the receivingtransducer becomes insignificant before it receives the irst vibrationenergy of the next transmitted pulsation.

References Cited in the file of this patent UNITED STATES PATENTS2,627,543 Obermaier Feb. 3, 1953 2,711,646 Mendousse June 28, 19552,724,269 Kalmus Nov. 22, 1955 2,739,478 Gtner Mar. 27, 1956 2,779,931Hersey Jan. 29, 1957 2,826,912 Kritz Mar. 18, 1958 2,874,568 PetermannFeb. 24, 1959 2,911,825 Kritz Nov. 10, 1959 2,911,826 Kritz Nov. 10,1959 2,912,856 Kritz Nov. 17, 1959 2,923,155 Welkowitz Feb. 2, 19602,959,054 Welkowitz Nov. 8, 1960 FOREIGN PATENTS 771,637 Great BritainApr. 3, 1957 776,526 Great Britain June 5, 1957

1. A SYSTEM FOR MEASURING FLUID FLOW IN A CONDUIT, SAID SYSTEM INCLUDINGA VIBRATION TRANSMITTING AND A VIBRATION RECEIVING TRANSDUCER COUPLED TOSAID CONDUIT, SAID TRANSMITTING TRANSDUCER BEING ORIENTED TO DIRECT AVIBRATION BEAM SUBSTANTIALLY TRANSVERSELY ACROSS THE CONDUIT IN THEABSENCE OF FLUID FLOW, MEANS FOR ENERGIZING SAID TRANSMITTING TRANSDUCERINTERMITTENTLY TO GENERATE A PULSED VIBRATION WAVE BEAM, MEANS COUPLEDTO SAID RECEIVING TRANSDUCER AND RESPONSIVE TO THE AMPLITUDE OF THERECEIVED WAVE, SAID RECEIVING TRANSDUCER BEING DISPLACED A SHORTDISTANCE FROM SAID TRANSMITTING TRANSDUCER ALONG THE PRINCIPAL AXIS OFSAID CONDUIT IN THE DIRECTION OF THE ORIGIN OF THE FLOW OF THE FLUIDTHROUGH THE CONDUIT WHERE IT INTERCEPTS THE VIBRATION WAVE PULSATIONSDIRECTED TRANSVERSELY OF THE CONDUIT AND ECHO PULSATIONS THEREOF, THEAMOUNT OF VIBRATION ENERGY RECEIVED BY THE RECEIVING TRANSDUCER VARYINGSUBSTANTIALLY WITH THE CHANGE IN THE FLOW OF THE FLUID AS THE VIBRATIONWAVE BEAM IS DEFLECTED BY THE MOVEMENT THEREOF, AND A FLUID FLOWINDICATING MEANS COUPLED TO SAID RECEIVING TRANSDUCER AND RESPONSIVE TOTHE OUTPUT OF SAID RECEIVING TRANSDUCER FOR INDICATING FLUID FLOW.